Fixed rail transportation systems, that include one or more rail vehicles traveling over spaced apart rails of a railway track, have been an efficient way of moving cargo and people from one geographical location to another. In densely populated countries and countries having unimproved road transportation systems, rail vehicles may be the primary means for moving people and cargo. Additionally, rail transportation is used in areas where little to no population exists. Accordingly, there are probably millions of miles of railroad track throughout the world that need to be maintained. Because road transportation is also prevalent, roads are known to bisect, and or cross, railway tracks. Typically, a crossing warning system is located where a road crosses railroad tracks. There are probably hundreds of thousands of crossing warning systems in operation today.
Most crossing warning systems currently used in the United States are crossing predictors. Crossing predictors provide a constant warning time of train arrival to motorists at the crossing, regardless of train speed. These are commonly used in the United States due to the many railroad lines with mixed traffic speeds (heavy freight vs. light passenger). Such systems do not take into account train direction. Such systems typically have only been concerned with constant warning. Thus, regardless of train direction, as a train moves towards a crossing, from either side, a measured impedance will decrease proportional to train speed. More specifically, these systems measure electrical impedance of the rail as a train moves towards the crossing. The rate of change of the impedance is proportional to the train speed, and along with the known distance of the crossing approach length, can be used to predict the estimated time to crossing of the train. Thus, these systems predict when the train will arrive at the crossing, thus providing a constant warning time to the motorist, regardless of varying train speed.
European crossing warning systems and a limited number of systems in the United States use axle counters or treadles to magnetically, or mechanically, count train axles. These sensors may be wired together on either side of the crossing to determine train direction. However, these systems have proven unreliable and expensive. Furthermore, they have proven not to provide constant warning to motorist.
New crossing monitoring systems are being developed to automatically record and document the performance of crossing warning devices as trains pass by, but these new systems do not readily lend themselves to determining a direction that a passing train is traveling. Thus, such new systems still require an additional element to be able to determine a direction a train is traveling.
Railroad owners and/or users of railroads spend a significant amount of time and money adhering to Federal Railroad Administration (FRA) mandated testing of crossing warning systems. The FRA requires monthly testing of crossing warning systems to insure that they operate properly. Since each approach track on either side of the crossing provides its own independent warning time, verification of these systems should be performed for trains traveling in both directions. These tests are generally performed manually, such as by waiting for a train to move through a crossing or by driving a railroad maintenance vehicle through a crossing and monitoring the warning time, gate/light/bell activation. Since the systems should be tested for vehicles approaching in each direction, either the testers must wait for trains to travel in both directions or drive their maintenance vehicles through the crossing in both directions. Performing these tests amounts to a significant amount of time and money, especially considering the number of active crossings that currently exist.
FIG. 1 depicts a prior art embodiment of a railroad crossing system 25. As illustrated, the railway rails 10 are intersected by a road crossing 12. On one side of the road crossing 12 a transmitter 13 is connected across the rails. On both sides of the road crossing a receiver 14, 15 is connected across the rails 10. One receiver 14 senses a transmit voltage, TV, and the other receiver 15 senses a receive voltage, RV. Furthermore, the transmit voltage receiver 14 may or may not share the same connections to the rails 10 as the transmitter 13.
The distance between the receivers 14, 15 is generally referred to as an island 18. Located on both sides of the road crossing 12 are termination shunts 16 which are connected across the rails 10. The termination shunts 16 contain transmitted signals that are associated with that section of the track 10. The distance between a termination shunt 16 and the closest transmitter 13 and/or receiver 14, 15 is commonly referred to as an approach 20. The approach 20 is effectively a surveillance area for the crossing predictor to monitor trains.
Thus, as a train moves towards the crossing 12, from either side, transmit voltage (TV) and receive voltage (RV) are monitored to calculate an electrical impedance seen by the crossing predictor. As the train gets closer, the electrical impedance decreases proportional to the speed of the train. This is due to the train wheel axles acting as an electrical shunt. Knowing the fixed approach distance, the speed of the train can be used to estimate a time the train will arrive at the crossing and provide constant warning time, such as but not limited to, by activating lights, gates, bells, etc. 9, to a motorist at the road crossing 12, regardless of train speed.
A solution is therefore needed for determining a direction a vehicle is traveling on a railway track as it approaches a road crossing so that the significant amount of time and money spent by Railroad owners and/or users of railroads adhering to requirements, such as those mandated by the FRA, to test crossing warning systems is limited.